Reciprocating pump systems, such as sucker rod pump systems, extract fluids from a well and employ a downhole pump connected to a driving source at the surface. A rod string connects the surface driving force to the downhole pump in the well. When operated, the driving source cyclically raises and lowers the downhole pump, and with each stroke, the downhole pump lifts well fluids toward the surface.
For example, FIG. 1 shows a sucker rod pump system 10 used to produce fluid from a well. A downhole pump 14 has a barrel 16 with a standing valve 24 located at the bottom. The standing valve 24 allows fluid to enter from the wellbore, but does not allow the fluid to leave. Inside the pump barrel 16, a plunger 20 has a traveling valve 22 located at the top. The traveling valve 22 allows fluid to move from below the plunger 20 to the production tubing 18 above, but does not allow fluid to return from the tubing 18 to the pump barrel 16 below the plunger 20. A driving source (e.g., a pump jack or pumping unit 30) at the surface connects by a rod string 12 to the plunger 20 and moves the plunger 20 up and down cyclically in upstrokes and downstrokes.
During the upstroke, the traveling valve 22 is closed, and any fluid above the plunger 20 in the production tubing 18 is lifted towards the surface. Meanwhile, the standing valve 24 opens and allows fluid to enter the pump barrel 16 from the wellbore.
At the top of stroke, the standing valve 24 closes and holds in the fluid that has entered the pump barrel 16. Furthermore, throughout the upstroke, the weight of the fluid in the production tubing 18 is supported by the traveling valve 22 in the plunger 20 and, therefore, also by the rod string 12, which causes the rod string 12 to stretch. During the downstroke, the traveling valve opens, which results in a rapid decrease in the load on the rod string 12. The movement of the plunger 20 from a transfer point to the bottom of stroke is known as the “fluid stroke” and is a measure of the amount of fluid lifted by the pump 14 on each stroke.
At the surface, the pump jack 30 is driven by a prime mover 40, such as an electric motor or internal combustion engine, mounted on a pedestal above a base 32. Typically, a pump controller 60 monitors, controls, and records the pump unit's operation. Structurally, a Sampson post 34 on the base 32 provides a fulcrum on which a walking beam 50 is pivotally supported by a saddle bearing assembly 35.
Output from the motor 40 is transmitted to a gearbox 42, which provides low-speed, high-torque rotation of a crankshaft 43. Both ends of the crankshaft 43 rotate a crank arm 44 having a counterbalance weight 46. Each crank arm 44 is pivotally connected to a pitman arm 48 by a crank pin bearing 45. In turn, the two pitman arms 48 are connected to an equalizer bar 49, which is pivotally connected to the rear end of the walking beam 50 by an equalizer bearing assembly 55.
A horsehead 52 with an arcuate forward face 54 is mounted to the forward end of the walking beam 50. As is typical, the face 54 may have tracks or grooves for carrying a flexible wire rope bridle 56. At its lower end, the bridle 56 terminates with a carrier bar 58, upon which a polished rod 15 is suspended. The polished rod 15 extends through a packing gland or stuffing box at the wellhead 13. The rod string 12 of sucker rods hangs from the polished rod 15 within the tubing string 18 located within the well casing and extends to the downhole pump 14.
As is known, pump jack operating characteristics are typically characterized by the American Petroleum Institute (“API”) Specifications, which expresses parameters as a function of the geometry of a pumping unit's four-bar linkage. Standardized API linkage geometry designates: dimension “A” as the distance from the center of the saddle bearing 35 to the centerline of the polished rod 15; dimension “C” as the distance from the center of the saddle bearing 35 to the center of the equalizer bearing 55; dimension “P” as the effective length of the pitman arm 48 as measured from the center of the equalizer bearing 55 to the center of the crank pin bearing 45; dimension “R” as the distance from the centerline 43 of the crankshaft to the center of the crank pin bearing 45; dimension “H” as the height from the center of the saddle bearing 35 to the bottom of the pump jack base 32; dimension “I” is the horizontal distance from the center of the saddle bearing 25 to the centerline 43 of the crankshaft; dimension “G” as the height from the centerline 43 of the crankshaft to the bottom of the pump jack base 32; and dimension “K” as the distance from the centerline 43 of the crankshaft to the center of the saddle bearing 35. Dimension “K” may be computed as:K=√{square root over ((H−G)2+I2)}
As is typical, the pump jack 30 as in FIG. 1 operates in conjunction with a vertically aligned wellhead 13. In some implementations, portions of a wellbore may be inclined or slanted from a vertical angle. In general, the slanted wellbore can penetrate fluid producing strata of a formation along a longer path for more exposure to the producing formation. Therefore, depending on the well's depth, the wellhead 13 at surface may also be inclined relative to vertical. The range of surface inclination typically varies between 0 and 45 degrees from vertical (i.e., between 90 and 45 degrees relative to the horizontal surface).
Apart from all of the complications downhole, the slanted wellhead and wellbore present problems for a traditional pump jack at surface. One configuration of a pump jack 30 for use with a slanted well having an inclined wellhead 13 is shown in FIG. 2A. (The same reference numerals are used for similar components described in previous figures.) This configuration is similar to that disclosed in U.S. Pat. No. 4,603,592. As shown, the wellhead 13 is inclined at an angle θ relative to the horizontal surface S. To direct the polished rod 15 through the slanted wellhead 13, the orientation of the walking beam 50 has been tilted. In particular, the pitman arms 48 have a longer length, the Sampson post 34 is tilted forward, and the horsehead 54 may be enlarged so that the pumping unit 30 can address the inclined wellhead 13.
This configuration alters the geometry of the four-bar linkage of the pump jack 30 so that the polished rod 15 can align with the inclined wellhead 13. Unfortunately, the alteration of the four-bar linkage may have a significant effect on the operating characteristics of the pumping unit 30, such as changing the allowable polished rod load, changing the shape of the permissible load envelope, altering the length of the pumping stroke, inducing a phase angle shift in the counterbalance, etc. Moreover, the change in operating characteristics at surface may further affect controls, analysis, diagnostics of the downhole rod pump because calculations for these features are typically based on the standard four-bar linkage (K-R-P-C).
Another configuration of a pump jack 30 for use with a slanted well having an inclined wellhead 13 is shown in FIG. 2B. (The same reference numerals are used for similar components described in previous figures.) This configuration is similar to that disclosed in U.S. Pat. No. 8,240,221. Instead of increasing the length of the pitman arms 48, this configuration has an elbow-shaped walking beam 50 to address the angled wellhead 13. The elbow shape is formed by a bend or elbow section 53 that defines forward and rearward sections of the beam 50. The bend 53 is located forward of the centerline of the center bearing 35.
The forward section of walking beam 50 is fabricated so its longitudinal axis is angled to address the inclination of the wellhead 13. In this way, the radius A from the centerline of the center bearing 35 to the arcuate face 54 of the horsehead 52 is tangent to the inclined polished rod 15. As disclosed, the non-linear bent walking beam 50 is described as providing a simple and effective means of addressing the angled wellhead 13 while preserving the operating characteristics of a prior art pumping unit. As also disclosed, the beam 50 is fabricated with the bend 53 that closes matches the wellhead angle. As further disclosed, the rearward section of the walking beam 50 from the saddle bearing 35 to the equalizer bearing 55, and the four-bar linkage system embodied by the pump jack, remains unchanged relative to a prior art pump jack intended for vertical wells.
Although slant well pump jacks of the prior art may have some benefits, operators are continually striving to increase the versatility of pump jack systems to meet the challenges of various implementations. The subject matter of the present disclosure is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above.